A density variation correction method for a printing system includes printheads in at least one linehead printing a test block pattern on a print media. A density variation trace is produced for each printed test block in the test block patterns by capturing an image of each test block and averaging pixel data in a transport direction. The density variation traces associated with a known print density represented in the test block pattern are compared with a respective reference density value. A determination is made as to whether there is a difference between each density variation trace and the respective reference density value. If there is a difference, the density variation trace is adjusted to match the reference density value. The method can be repeated for all of the known print densities represented in the test block pattern and for all of the lineheads in the printing system.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A method for density variation correction in a printing system that includes a linehead that jets ink onto a moving print media and an integrated imaging system that captures images of content printed on the moving print media, wherein the linehead includes a plurality of printheads, the method comprising: (a) using each printhead to print a test block pattern on the print media, wherein the test block pattern includes test blocks having different known print densities, each test block having a respective reference density value; (b) producing a first individual density variation trace for each printed test block in the test block patterns printed by each of the plurality of printheads by capturing an image of each test block and averaging pixel data in a transport direction; (c) comparing the first individual density variation traces with the respective reference density values; (d) determining whether there is a difference between each first individual density variation trace and the respective reference density value; (e) adjusting the first individual density variation traces in accordance with the determined difference by changing the ink lay down quantity provided by each printhead to adjust print values corresponding to the test block pattern printed by the plurality of printheads to match the respective reference density value, thereby producing printed densities that are substantially the same as the reference density values; (f) using each printhead in response to its adjusted individual density variation trace to print an adjusted test block pattern on the print media; (g) producing a second individual density variation trace for each printed test block in the adjusted test block pattern printed by each of the plurality of printheads; (h) determining an average density variation trace based upon the second individual density variation traces; and (i) adjusting the second individual density variation traces to match the average density variation trace by changing the ink lay down quantity provided by each printhead to thereby correct density variation.
2. The method as in claim 1 , wherein producing a first individual density variation trace for each printed test block in the test block patterns by capturing an image of each test block and averaging pixel data in a transport direction comprises producing a first individual density variation trace for each printed test block in the test block patterns by capturing an image of each test block and optically averaging pixel data in a transport direction.
3. The method as in claim 1 , wherein (a) using each printhead to print a test block pattern on the print media comprises using each printhead to print a test block pattern on the print media using flat field corrected print data values.
4. The method as in claim 1 , further comprising (i) storing the first individual density variation trace or adjusted first individual density variation trace in a storage device.
5. The method as in claim 1 , wherein (e) adjusting the first individual density variation traces in accordance with the determined difference further comprises: determining whether the difference equals or exceeds a threshold value; and adjusting the first individual density variation traces only if the difference equals or exceeds the threshold value.
6. The method as in claim 1 , further comprising (i) storing the adjusted second individual density variation traces in a storage device.
7. The method as in claim 1 , further comprising (i) storing the average density variation traces in a storage device.
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June 29, 2012
August 12, 2014
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